1. Field
Embodiments of this invention relate generally to a semiconductor device suitable for power control, such as an IGBT (insulated gate bipolar transistor), IEGT (injection enhanced gate transistor), MOSFET (metal-oxide-semiconductor field effect transistor), super junction MOSFET.
2. Background Art
Power semiconductor devices are required to have high breakdown voltage in view of their application. To ensure high breakdown voltage, vertical devices need a thick high-resistance base layer, and lateral devices need a long high-resistance base layer. As the breakdown voltage rating of a device becomes higher, the device needs a thicker or longer high-resistance base layer in proportion to its blocking voltage rating. However, although increase in the thickness or length of the high-resistance base layer can indeed provide a higher breakdown voltage, it results in degradation of on-resistance and switching characteristics. Thus, if the same blocking breakdown voltage can be realized, the structure of a power semiconductor device is desirably such that the high-resistance base layer can be designed to be thinner or shorter.
On the other hand, power semiconductor devices can be classified into the punch-through type and non-punch-through type from the viewpoint of breakdown voltage design. In some applications, power semiconductor devices may need forward and reverse blocking breakdown voltage. However, on a device with the punch-through structure, it is difficult to realize comparable blocking breakdown voltage in the forward and reverse direction. Hence, it is conventionally necessary to use the breakdown voltage design of the non-punch-through type in which the high-resistance base layer is thicker or longer than the width of the depletion layer under application of rated voltage, at the expense of on-resistance and switching characteristics.
As disclosed in Japanese Patent No. 3281194, the present inventor proposed a power semiconductor device having low on-resistance, good switching characteristics, and high forward and reverse breakdown voltage. As a result of subsequent studies, the inventor has found how it is specifically designed to respond to practical requirements.